Wavelength division multiplexing system and method using reconfigurable diffraction grating

ABSTRACT

An improvement in a wavelength division multiplexer and/or a dense wavelength division multiplexer (WDM/DWDM) is achieved by incorporating an electronically reconfigurable diffraction grating (108). The introduction of the electronically reconfigurable diffraction grating (108), which is typically fabricated using MEMS (microelectromechanical systems) technology, improves the compact design, durability, and dynamic functionality of the WDM/DWDM system.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application U.S. Ser. No.09/455,093 filed Dec. 6, 1999, 1999, now U.S. Pat. No. 6,421,179 issuedJul. 16, 2002, and is also a U.S. national stage application (35 USC371) based on PCT/US00/42560 filed Dec. 5, 2000. Said U.S. Ser. No.09/455,093 is a continuation-in-part of application Ser. No. 09/069,502,filed Apr. 29, 1998, which in turn claims the benefit of U.S.Provisional Application No. 60/045,483, filed May 2, 1997.

FIELD OF THE INVENTION

This invention relates to the field of wavelength division multiplexingand dense wavelength division multiplexing/demultiplexing, andparticularly to the use of reconfigurable diffraction gratings in bothfields.

BACKGROUND OF THE INVENTION

Wavelength Division Multiplexing (WDM) and Dense Wavelength DivisionMultiplexing (DWDM) systems are important components in fiber opticcommunication systems and networks. The essential component of suchsystems focus on the multiplexer/demultiplexer. Current alternativesinclude diffractive elements such as dielectric thin film filters,arrayed waveguide gratings and fiber Bragg gratings, each possessingtheir own advantages and disadvantages for a particular system design.Overall it is desirable in such a system or network application tominimize crosstalk between channels by maximizing channel isolation.This task becomes increasingly more difficult in all fiber DWDM systemswhere channel spacing and bandwidth is very small. (Pan, Shi, and Loh,WDM Solutions, Laser Focus World Supplement, September 1999, pp. 15–18.)Prior art technology is primarily comprised of devices and systemsutilizing the aforementioned diffractive elements, and attention isoften given to improving resolution of the system while minimizingcrosstalk by improving other system components such as the fiber opticchannels.

Reconfigurable multiplexing devices can be achieved in a variety ofways. Several such prior art devices have different levels ofreconfigurability, functionality and performance. For example, U.S. Pat.No. 5,245,681 discloses a reconfigurable wavelength multiplexing devicethat relies on a fiber optic tree structured switching matrix to providethe reconfigurability of the system. The switching matrix is comprisedof several stages of optical couplers that are controlled by theapplication of a specified voltage. The voltage application is used tocontrol the passage of light through the coupler. The ability to turn onand off the voltages to the individual couplers in the matrix make thedevice reconfigurable.

U.S. Pat. No. 5,550,818 utilizes an optical fiber network ring in awavelength division multiplexing system. Cross-connecting switchingdevices control the signal routing through the system. Again, theswitches are based on voltage application to the switch.

U.S. Pat. No. 5,650,835 discloses a reconfigurable optical beamsplitterin which periods of optical phase shift regions are established across aliquid crystal cell to form an optical grating in the liquid crystalthat will perform as a multiplexing or demultiplexing device. Thedesired pattern of phase shift regions across the cell is accomplishedby applying corresponding voltage differentials across the cell whichcan be dynamically reconfigured.

U.S. Pat. No. 5,771,112 provides a reconfigurable device for theinsertion and the extraction of wavelengths utilizing a main opticalswitch connected to a specified number of add/drop multiplexers.

U.S. Pat. No. 5,712,932 provides a dynamically reconfigurable wavelengthdivision multiplexer. The reconfigurable optical routing system isachieved by using fiber-based Bragg grating or a wavelength selectingoptical switch in combination with a fiber optic directional coupler.

All of the above-noted prior art relies primarily on some form of anoptical switch to allow or disallow signal passage through anestablished route in the network or system. However, these systems arelimited in their ability to redirect a specified wavelength through adifferent route in the system. An improvement that enables suchrerouting would have direct application in and benefits to thecommunications industry.

A key component in a WDM/DWDM system is the means of separating theincident light by wavelength. Although there are many means toaccomplish this, recent advances in micromachining technology have ledto the development of reconfigurable diffraction gratings that can beapplied to multiplexing. Such micromachined gratings can be used forvarious electro-optical applications such as multiplexing, spectroscopy,modulated display technology and optical signal processing.

A deformable grating apparatus is presented in U.S. Pat. Nos. 5,459,610and 5,311,360, both by Bloom et al. An array of beams, at initiallyequal heights and with reflective surfaces, are supported atpredetermined fractions of incident wavelength above a similarlyreflective base. Below the base is a means of electrostaticallycontrolling the position of the beams by supplying an attractive forcewhich will deflect all of the beams or every other beam to a secondaryposition. The diffraction of the incident light is dependent upon theposition of the reflective beam elements.

An electronically programmable diffraction grating is presented in U.S.Pat. No. 5,757,536 by Ricco, et al. A plurality of electrodes control aseries of grating elements whose upper surface diffract incident light.The grating is typically formed by a micromachining process.

Although reconfigurable in nature, the micromachined diffractiongratings discussed above are still limited in their useable bandwidthand the span of available wavelengths for at least the specifiedapplication of lightwave multiplexing and demultiplexing. Ideally, thereconfigurable diffraction grating used should at least permit virtuallyunlimited, dynamic wavelength selection, which the prior art does notpermit.

OBJECTS OF THE INVENTION

Therefore, it is the object of the invention disclosed herein to providean improved wavelength division multiplexer (WDM) using anelectronically reconfigurable diffraction grating.

It is also an object of the invention to provide an improved densewavelength division multiplexer (DWDM) using an electronicallyreconfigurable diffraction grating.

It is also an object of the invention to provide an improved WDM/DWDMsystem using an electronically reconfigurable diffraction gratingcapable of dynamic reconfigurability of output.

It is also an object of the invention to provide an improved WDM/DWDMsystem capable of simultaneous demultiplexing and optical switchingfunctions.

It is also an object of the invention to provide an improved WDM/DWDMsystem capable of demultiplexing input light over an increased opticalwaveband range.

SUMMARY OF THE INVENTION

The invention disclosed herein in several embodiments provides animprovement in a wavelength division multiplexer and/or a densewavelength division multiplexer (WDM/DWDM) by incorporating anelectronically reconfigurable compound diffraction grating into theoverall multiplexing apparatus or system. The introduction of anelectronically reconfigurable compound diffraction grating, which istypically fabricated using MEMS (microelectromechanical systems)technology, improves the compact design, durability, and functionalityof the WDM/DWDM system.

In particular, the electronically reconfigurable compound diffractiongrating improves upon alternative wavelength separation technology suchas dielectric filters, arrayed waveguide gratings, and fiber Bragggratings, which all limit WDM/DWDM systems regarding channel separationand channel. The present invention allows individual channels orwavelengths to be automatically switched between different systemdetectors. The optical switching functions, and also themultiplexing/demultiplexing functions, are both incorporated in a singledevice. This adds tremendous flexibility to an optical network. Thereconfigurable compound diffraction grating has the necessary resolutionto be useful for both WDM and DWDM applications.

In the preferred embodiment, this optical wavelength divisionmultiplexing apparatus comprises a reconfigurable diffraction gratingdiffracting at least one input light beam into diffracted light beams ofN wavebands wherein N is an integer greater than zero; and furtherdiffracting each of these input light beams into diffracted light beamsacross X diffraction orders wherein X is an integer greater than zero,for each of these N wavebands.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention believed to be novel are set forth in theassociated claims. The invention, however, together with further objectsand advantages thereof, may best be understood by reference to thefollowing description taken in conjunction with the accompanyingdrawings in which:

FIG. 1 is a two dimensional cross-sectional schematic view of thewavelength division multiplexer utilizing a reconfigurable diffractiongrating to diffract light to the first order and alternatively to thesecond order.

FIG. 2 is a top view of the preferred mode of an electronicallyreconfigurable diffraction grating for use in accordance with theinvention.

FIG. 3 is a two dimensional side view of a deflectable beam andstationary beam in an initial position of one embodiment of thepreferred mode of the reconfigurable compound diffraction grating foruse in accordance with the invention.

FIG. 4 is an exploded three dimensional view of one embodiment of thepreferred mode of the electronically reconfigurable compound diffractiongrating, in its initial position.

FIG. 5 is an exploded three dimensional view of one embodiment of thepreferred mode of the electronically reconfigurable compound diffractiongrating, in its energized position.

FIG. 6 is a schematic cross sectional view of an embodiment of thepreferred mode of the reconfigurable diffraction grating wherein everyother diffraction beam is deflectabie beam with an associated lowerelectrode extension beam.

FIG. 7 is a schematic cross sectional view of another embodiment of thepreferred mode of the reconfigurable compound diffraction gratingwherein every third beam is a deflectable beam with an associated lowerelectrode extension beam.

FIG. 8 is a schematic cross sectional view of another embodiment of thepreferred mode of the reconfigurable compound diffraction gratingwherein every fifth beam is a deflectable beam with an associated. lowerelectrode extension beam.

FIG. 9 is a schematic cross-sectional view of another embodiment of thepreferred mode of the reconfigurable diffraction grating wherein everybeam is a deflectable beam with an associated lower electrode extensionbeam.

FIGS. 10 and 11 are representations of light diffracting from a suitableembodiment of the reconfigurable compound diffraction grating in itsinitial undeflected position (FIG. 10) and its secondary energizedposition (FIG. 11).

DETAILED DESCRIPTION

The primary basic function of a wavelength division multiplexer or densewavelength division multiplexer (WDM/DWDM) is to provide a means ofwavelength separation to a fiber optic communication system or network.Input light is separated into a plurality of channels with typicallynarrow width and wavelength separation. Therefore each channel isdesignated a specific spectral bandwidth that can be detected ormonitored. A dense wavelength division multiplexer is a more specificclass of wavelength division multiplexer in which the channel width andseparation is extremely narrow. The WDM/DWDM can be utilized with avariety of light input sources, typically broadband from a series ofnarrow band sources, or from a single broadband source, introduced fiberoptically to the network. The single most important feature of such asystem is the ability to accurately and precisely separate the incominglight on the receiver end of the fiber into the desired number ofchannels at the specified wavelengths and spectral widths, and also toproperly deliver that light energy to the desired detector or sensor. Asthe light is separated by wavelength, it is important to minimizeinsertion loss and channel crosstalk.

The present invention provides an improved WDM/DWDM that utilizes areconfigurable compound diffraction grating. A “compound” diffractiongrating is a diffraction grating which effectively combines andinterleaves two or more grating structures at different positions in thesame physical space, in a way that will become clearer from thedisclosure herein. In addition to multiplexing capabilities, the presentinvention provides for optical switching of the multiple channel outputsbetween at least two different sets of photodetectors. In this way, itessentially combines the function of a WDM and an optical switch into asingle compact device.

FIG. 1 is a two dimensional operational schematic of the WDM/DWDMaccording to the invention. Optical input means such as fiber 100introduces light source energy into the system. As mentioned above, theinput means 100 is capable of providing light, for example, from aseries of narrowband sources, or from a single broadband source, to thesensor network. The dispersed input source light 102 is collected by afirst system focusing means (e.g., lens) 104 such as the illustratedlens. The first system focusing means 104 is ideally located a focallength away from input means 100 end so as to produce collimated inputlight 106 comprising at least one input light beam which impinges uponthe reconfigurable compound diffraction grating 108. This configurationadds to the efficiency of the system or network by minimizing the numberof optical components in the system and maximizing the energy throughputof the system.

Reconfigurable compound diffraction grating 108, it will be observed, isa reflection-type grating where the diffracted output light emerges fromthe same side of the grating structure that the input light enters, asopposed to a transmission-type grating where light enters one side ofthe grating structure, is diffracted, and then emerges out the otherside.

As stated above and elaborated below, reconfigurable compounddiffraction grating 108 not only separates light by wavelength formultiplexing, but enables switching among multiple photodetectors byusing various diffractive orders of the diffracted light. The specificoperation of a preferred mode for reconfigurable compound diffractiongrating 108 will be described in detail below, but other less-preferred,yet still suitable grating structures can also be employed within thescope of this disclosure and its associated claims.

FIG. 1 illustrates reconfigurable compound diffraction grating 108separating collimated input light 106 into only two wavelengths in onlythe first order and second order, just to simplify the drawing. It isunderstood and hereby disclosed, however, that reconfigurable compounddiffraction grating 108 can separate the incoming light into Ndistinctly separate channels. It is also understood and hereby disclosedthat reconfigurable compound diffraction grating 108 can diffract thelight into a single order or multiple orders ranging from the firstorder to X higher orders (the zero order is also available as well).These variables N and X are functions of the design of thereconfigurable compound diffraction grating 108, and will be describedin detail below.

FIG. 1 thus illustrates a sample, not limiting, situation wherein thediffraction of light is completely directed to the first order as shownin the solid-line trajectory, or optionally to the second order as shownby the dotted-line trajectory. Again, only the first two orders areshown for simplicity, but the invention extends into X higher orders aswell. The optical switching between and among the orders, and thusbetween and among various detectors, of all or part of the input light,is a distinct advantage enabled only by the incorporation ofreconfigurable compound diffraction grating 108 into the WDM/DWDM.

As detailed in FIG. 1, a diffracted light beam of a first wavelength ofa first input light beam is diffracted to first order 110 by thereconfigurable compound diffraction grating 108. Similarly, a diffractedlight beam of second wavelength of the first input light beam isdiffracted to first order 112. Further, reconfigurable compounddiffraction grating 108 similarly diffracts a diffracted light beam ofsaid first wavelength of a second input light beam to first order 114,and a diffracted light beam of said second diffracted wavelength of thesecond input light beam to first order 116. Again, for simplicity, onlytwo input beams and associated diffracted beams are shown in FIG. 1. Itwould be understood by someone of ordinary skill the collimated inputlight 106 is incident on and diffracted from the entire surface of thereconfigurable compound diffraction grating 108 and thus comprisesnumerous input light beams.

All of the first order diffracted light beams (110, 112, 114, and 116)are collectively focused by a first order focusing means (e.g. lens)118, to a first order, first wavelength output means (e.g. fiber) 120and a first order, second wavelength output means (e.g. fiber) 122.Typically the output means (120 and 122), e.g., fibers, are componentsof a larger first order set of output means 140 such as a first orderoutput fiber array that is coupled to a first order optical detectionmeans 142. This figure is representative of the operation of theinvention, and again, is considered to include N output fibers in theoutput fiber array/bundle, with each fiber corresponding to and carryingone of the N diffracted wavelengths or wavebands. Each wavelength orwaveband is then delivered to one of at least N regions of opticaldetector 142, each said region receiving and detecting that wavelength.

As stated above, reconfigurable compound diffraction grating 108 canalso be configured to wholly or partially diffract light into any of thehigher orders so as to specify wavelengths for individual detectors. InFIG. 1, the alternative of diffracting light into the second order isdemonstrated by the dotted trajectory. This also can be extended intohigher orders, with multiple detectors available to the system, and theseparation by order serving to implement an optical switchsimultaneously with multiplexing by wavelength or waveband.

Continuing the detailed description of FIG. 1, therefor, the firstwavelength of the first light beam is also diffracted to second order124, as is the second wavelength of the first light beam also diffractedto second order 126. In addition, reconfigurable compound diffractiongrating 108 similarly diffracts the first wavelength of the second lightbeam to second order 128, and the second wavelength f the second lightbeam to second order 130.

Similarly to what was earlier described for first order, the secondorder input light beams (124, 126, 128, and 130) are collectivelyfocused by a second order focusing means (e.g., lens) 132 to a secondorder, first wavelength output means (e.g. fiber) 134 and a secondorder, second wavelength output means (e.g. fiber) 136. Typically theoutput fibers (134 and 136) are components of a larger second order setof output means 144 such as a second order output fiber array/bundle,coupled to a second order optical detection means 146.

As stated above, this figure is a simplified representation of theoperation of the reconfigurable compound diffraction grating 108 inorder to clearly demonstrate the diffraction into wavelengths andorders. It is understood that the reconfigurable compound diffractiongrating 108 is capable of diffracting light along the entire length ofthe grating into any specified order among the X orders, and ofseparating that light into N wavelengths, as determined by its specificdesign. This figure is representative of the operation and the inventionis thus considered to include N output fibers in the output fiberarray/bundle, each fiber corresponding to one the N diffractedwavelengths or wavebands, as well as X optical detection means and Xfiber arrays/bundles, one for each of the X orders.

The optical components used in FIG. 1 to provide collimated light input106 to reconfigurable compound diffraction grating 108 is a simple firstsystem lens 104 placed a focal length away from the input fiber 100.Alternatives to the preferred embodiment include more complex means ofcollimating optics including multi-element lens systems that providesimilar means of collimation in a more complex design where thepossibility of optical transmission loss needs to be compensated by amore sophisticated lens system.

The preferred embodiment includes the utilization of output fibers (i.e.120, 122, 134, 136), typically as part of a fiber optic array or bundle(i.e. 140, 144), to collect the individual wavelengths produced by theoverall system. The use of output fibers minimizes space requirements inthe multiplexer design and allows easy direction of individual ormultiple wavelength output to specific optical detection means (i.e.142, 146).

In an alternative embodiment, individual optical detectors can be placeddirectly at the focus of the first or second order lens (118 or 132,respectively) to collect the output directly, and fibers (i.e. 120, 122,134, 136) and fiber bundles (i.e. 140, 144) omitted from FIG. 1.

Optical detection means (i.e. 142, 146) capture the intensity of theindividual channels of the WDM/DWDM system. Typically intensitydetectors comprise individual photodiodes, or alternatively detectorarrays such as CCD's or CID's. The optical detection means can be eitheranalog or digital, but primarily serves to measure the intensity of thesignal produced by the individual channels of the system represented bythe individual output fibers.

Before discussing the details of reconfigurable compound diffractiongrating 108, it is helpful to clarify the use of the terms “wavelength,”“waveband,” and “channel” as used herein. In the art, a waveband isoften a light signal comprising one or more wavelengths that are fairlyclose to one another, i.e., comprising one or more wavelengths within agiven narrow range of wavelengths defining the waveband. A “channel” isfrequently used to describe the carriage of a single such “waveband”comprising one or more “wavelengths.”

As used in this disclosure, the term “waveband” is to be broadlyinterpreted and understood as comprising one or more wavelengths closeto one another which are suitable for grouping together in a singlewaveband and carriage over a single channel such as a single fiber.Thus, each of the N “wavelengths” or “wavebands” diffracted at a givenorder by the reconfigurable compound diffraction grating specifiedherein are to be understood and interpreted as comprising one or morewavelengths close to one another, and are not to be understood orinterpreted as comprising only a single wavelength. Thus, a diffractiongrating which diffracts two or more close but distinct “wavelengths”toward a single one of the N optical fibers and/or N detector regions asdisclosed herein, would be considered as diffracting a single wavebandtoward that single optical fiber or detector region.

In the claims herein, it is to be observed that the term “waveband” isemployed throughout, and that this term is to be understood and definedas comprising possibly only one wavelength of light, but alternativelyas comprising two or more close but distinct wavelengths of light withina single defined wavelength band.

It is also to be observed that the foregoing discussion and the claimsrefer to N regions of the detectors 142 and 146. It is to be understoodthat detectors, such as photodiodes, are typically unitary entities anddo not have any distinctly defined regions associated therewith. Thereare also detectors that comprise an array of distinct elements orpixels, such as CCD's, whereas these elements could be construed asregions of the detector. However, in the present invention, once lighthas been separated (demultiplexed) into N distinct wavelengths orwavebands as described above, this separated light will be directedtoward and ultimately impinge on a detector. As it impinges on thedetector, the light itself in effect defines N regions of the detectorfor the present invention by virtue of its N distinctly separatewavelengths or wavebands impinging on the detector. That is, a givensingle region of the detector comes into being and is defined by thefact that a given single wavelength or waveband of separated light isdirected to and ultimately strikes upon that given single region of thedetector, and not by any inherent “regional” property of the detectoritself.

And finally, it is to be observed that the terms “multiplexing” and“demultiplexing” are typically used in the literature together, as inreferring to a multiplexing/demultiplexing system. In a technical sense,however, multiplexing refers to the combining or splicing together ofseparate wavelengths or wavebands into a single light signal, whiledemultiplexing refers to the splitting of a light signal into separatecomponent wavelengths or wavebands. Thus, the system illustrated anddescribed in FIG. 1 is really a demultiplexer in the technical sense ofthat term. However, given the tendency for these two terms to be usedtogether somewhat interchangeably in the art and in the literature, andthe common and accepted use of “multiplexing system” to refer to asystem that demultiplexes multiplexed signals, the term “multiplexingsystem” is what has been selected to refer in categorical terms to theinvention disclosed herein.

At this point, we turn to the diffraction grating itself. The primarybasic function of a diffraction grating in any application is toseparate incident light by wavelength. A diffraction grating in generalis sensitive to the wavelength and input angle of incident light, andits primary operation is to diffract specific wavelengths of light atspecific angles based on the grating design.

The preferred mode of reconfigurable compound diffraction grating 108used in the preferred embodiment of the invention is shown from a topview in FIG. 2 and exploded cutaway isometric views in FIGS. 4 and 5. Abase 248, typically made of silicon, supports a frame 250. A lowerelectrode lead 252 lies on the base 248, and runs parallel to and belowthe frame 250, as shown in FIG. 4. An upper electrode lead 254, runsthrough two corners of the frame 250 along the top surface 350 (seeFIGS. 4 and 5) of said frame 250, generally perpendicular to theextension of a set of diffraction beams 256 supported at their ends bythe frame 250.

In one set of embodiments, this set of diffraction beams 256 comprisesboth stationary beams 358 and deflectable beams 360, as shown in FIGS. 3through 8. In another embodiment, shown in FIG. 9, all of thediffraction beams 256 are deflectable beams 360. In all embodiments,diffraction beams 256 run substantially parallel to each other andsubstantially perpendicular to the sides of the frame 250, by which theyare supported. Diffraction beams 256 are of substantially uniformthickness, width and length. Diffraction beams 256 are much longer thanthey are wide and thick, and are spaced along frame 250 at periodicintervals. Both the base 248, and the top surface of the set of beams256, are of a reflective nature.

The upper electrode lead 254, the top surface 350 of the frame 250, andthe set of beams 256 are all electrically connected, and togethercomprise an upper electrode. The lower electrode lead 252 and a seriesof lower electrode extension beams 362 are all electrically connected,and together comprise a lower electrode. The frame 250, which is anelectrical insulator, enables the introduction of voltage differentialsbetween the upper electrode comprising 254, 350 and 256, and the lowerelectrode comprising 252 and 362.

The deflectable beams 360 can be identified as those in the set of beams256 which have the lower electrode extension beams 362 runningunderneath them. Also, in their initial undeflected position shown inFIG. 4 (see also FIGS. 6 through 9), the deflectable beams 360 are in anelevated plane above the stationary beams 358, although remaininggenerally parallel thereto. The relative parallelism is achieved by theexcessive length of all of the beams 256 as compared to their length andwidth. This elevation of the deflectable beams 360, and in particularthe reconfigurable, compound nature of this grating, is a key designfeature in of reconfigurable compound diffraction grating 108, which canbe viewed as the “compound” superposition of two grating structures. Theseries of deflectable beams 360, comprise a low resolution gratingsecondary to the higher resolution primary grating consisting of thefull set of beams 256.

In the embodiment of FIGS. 2 through 8, the “compound” superposition ofthis grating structure is built in by the prefabrication of elevateddeflectable beams 360 having lower electrode extension beams 362 runningunderneath them, and of stationary beams 358 defining a plane slightlybelow that of deflectable beams 360 and not having any lower electrodeextension beams 362 associated therewith. In the embodiment of FIG. 9,which will be elaborated further below, all of the beams are deflectablebeams 360, there are no stationary beams 358, and the “compound”structure wherein one set of beams is elevated with respect to anotherset of beams is achieved by applying a voltage differential to one setof beams while applying different voltage differentials (or no voltagedifferentials) to other sets of beams. In all embodiments, the system isreconfigured, at will, by a suitable application of voltagedifferentials to suitable set of diffraction beams 256. The embodimentof FIG. 9 is the most general, for so long as the voltage differentialthat can be applied to each diffraction beam 256 is individuallycontrollable, the overall grating structure can be actively reconfiguredin any chosen manner whatsoever.

Thus, in FIGS. 2 through 8, the diffraction of incident light byreconfigurable compound diffraction grating 108 is controlled bymanipulating the vertical position of particular individual beams in theset of beams 256, and in particular, by changing the vertical positionof the deflectable beams 360 while leaving unaltered the verticalposition of the stationary beams 358. In FIG. 9, this is achieved bychanging the vertical position of one set of beams, while leaving thevertical position of other sets of beams unaltered or differentlychanged.

FIG. 3 shows a cutaway side view of the interior of reconfigurablecompound diffraction grating 108 in which the vertical elevation of theplane of the deflectable beams 360, over the plane of the stationarybeams 358 is evident. One of the lower electrode extension beams 362 isshown lying on the base 248, immediately beneath one of the deflectablebeams 360. This deflectable beam 360 is shown in its initial position.As seen in FIG. 3, the majority of the top surface of the deflecteddeflectable beam 360, remains substantially parallel to an adjacentstationary beam 358. Application of a voltage differential between thedeflectable beams 360, and the lower electrode extension 362, results ina deflection of the beams 360, in which they approach the plane of thestationary beams 358. Of course, application of different voltages wouldresult in different degrees (distances) of deflection.

FIG. 4 is a cutaway isometric view of the reconfigurable compounddiffraction grating 108 in an initial, undeflected position. This viewshows exactly how the lower electrode extension beams 362 project alongthe base 248 from the lower electrode lead 252, and how the deflectablebeams 360 are positioned directly above the lower electrode extensionbeams 362 so that they may be deflected when a voltage differential isapplied between the upper and lower electrodes generally.

FIG. 5 is a similar cutaway isometric view of the reconfigurablecompound diffraction grating 108, with the deflectable beams 360depicted at a deflected position in which the deflectable beams 360 arein the same plane as the stationary beams. Applying a voltagedifferential across the two (upper and lower) electrodes via the upperand lower electrode leads 254 and 252, respectively, causes thedeflectable beams 360 to move towards the lower electrode extensionbeams 362. The deflection of the deflectable beam 360, is proportionalto the voltage applied to the lower electrode lead 252, and therefore tothe lower electrode extension beam 362 electrically connected thereto.The upper electrodes (comprising 254, 350, and 256 (i.e., 358/360)) aretypically fabricated as a unit whole with the rest of the gratingstructure typically of a material such as silicon. No shielding isnecessary between the stationary beams, 358, and the adjacentdeflectable beams, 360, since the aspect ratio of the set of beams, 256,is such that voltage applied to the lower electrode lead 252, andtherefore to the lower electrode extension beam, 362, is enough to onlydeflect the deflectable beam, 360.

Thus far, the stationary beams 358, and the deflectable beams 360 havebeen shown alternating every position in the diffraction grating, whichis represented in the cross sectional schematic view of FIG. 6.Alternative configurations of the stationary beams 358, and thedeflectable beams 360, may be desired depending on desired wavelengthrange. Although the diffraction of the incoming light is altered bychanging the vertical position of the deflectable beams 360, and therebychanging the vertical spacing between the stationary beams 358, and thedeflectable beams 360, alternative configurations of the stationarybeams 358 and the deflectable beams 360 are beneficial for various partsof the spectrum. In addition, such configurations can be determinedbased on the resolution requirements of the secondary grating structurethat comprises the deflectable beams 360.

FIG. 7 illustrates an alternative configuration in which the deflectablebeams 360 occupy every third position and the stationary beams 358occupy the remaining positions. Similarly, FIG. 8 illustrates anotheralternative configuration in which the deflectable beams 360 occupyevery fifth position and the stationary beams 358 occupy the remainingpositions. The alternative configurations are not limited to those shownin

FIGS. 6 though 8 respectively, a subset plurality of the diffractionbeams, namely deflectable beams 360, can be separated from one anotherby exactly one, two and four diffraction beams of another subsetplurality, namely stationary beams 358, of the diffraction beams, simplyby virtue of the basic grating structure configuration.

FIG. 9, shows another alternative configuration of the reconfigurablecompound diffraction grating 108 that could be beneficial to the designof the WDM/DWDM system, and which in fact is the most general. Thisemploys a lower electrode extension beam 362 under every beam in the setof beams 256, thereby making every beam a deflectable beam 360, whereinsome of the beams 256 are voltage deflected to a position appropriate tostationary beams 358, while others are voltage deflected to a positionappropriate to deflectable beams 360, as earlier described. With thisdesign, the voltage applied to the lower electrode leads 252 can becontrolled to individually address each lower electrode extension 362 toactively reconfigure the diffraction grating to the appropriateconfiguration (every other, every third, every fifth, etc.) for thespecified wavelength distribution to appropriate detectors of theWDM/DWDM. Here, a subset plurality of the diffraction beams can beseparated from one another by exactly one, two, four, and indeed anynumber of diffraction beams of another subset plurality of thediffraction beams, by virtue of the voltage differentials applied.

Thus, in the embodiment of FIG. 9, each diffraction beam has one lowerelectrode extension beam associated therewith. This enables at least onesubset plurality of the diffraction beams to be moved from the initialposition thereof to the deflected position thereof in any desiredperiodic combination with respect to at least one other subset pluralityof the diffraction beams (reconfigurable periodicity). It furtherenables the deflected positions of at least one subset plurality of thediffraction beams to differ from the deflected positions of at least oneother subset plurality of the diffraction beams (reconfigurable compoundstructure).

In short, in its most general form, the embodiment of FIG. 9 usesvoltage differential application means enabling the application of aplurality of voltage differentials to be applied to a correspondingplurality of subsets of the diffraction beams, wherein these subsets canbe as small as a single beam, enabling full periodic and compoundreconfigurability. (This “individual voltage addressability” of thebeams is most suited to the FIG. 9 embodiment, but can also be utilizedwith other embodiments as well.) This advanced design is a naturalextension of the configurations of the reconfigurable compounddiffraction grating 108 presented herein and allows a singlereconfigurable compound diffraction grating to satisfy all possibleconfiguration requirements of the WDM/DWDM system.

Using as an example the configuration in which every third beam isdeflectable as in FIG. 7 (or in which the embodiment of FIG. 9 hasvoltages applied to it so as to configure an every-third-beamstructure), FIGS. 10 and 11 are respective representations of the lightdiffracted from the reconfigurable compound diffraction grating 108 inthe initial position (FIG. 10) and as the beams are deflected to thesecondary position where the deflected and stationary beams are aligned(FIG. 11). That is, FIG. 10 represents the initial position of FIG. 4,and FIG. 11 represents the secondary position of FIG. 5, but with theevery-third-beam spacing of FIG. 7. The diffraction is changed when thebeams are deflected due to the change in the position of the reflectivesurface. The purpose of these representations is to demonstrate thereconfigurability and operation of the reconfigurable compounddiffraction grating used to achieve the switching and wavelength orwaveband selection described for the WDM/DWDM in FIG. 1, and not in anyway to limit the disclosure or the associated claims.

FIG. 10 shows in detail, the light diffracted from the reconfigurablecompound diffraction grating base 248 in the initial position of theconfiguration wherein every third beam is deflectable. The secondarydiffraction grating comprising only the deflectable beams 360 causes thediffraction described below as due to 3 d spacing. The primarydiffraction grating consisting of the entire set of beams 256, accountsfor the diffraction described below as due to d spacing. The diffractioncapable of being generated from impinging light 1064 (which correspondsto one of the input light beams discussed in connection with FIG. 1),includes a zero order, 1066, a first order (due to 3 d spacing where dis beam spacing), 1068, a second order (due to 3 d spacing), 1070 and athird order/first order superposition (due to 3 d spacing and d spacing,respectively), 1072. In this example, the first order 1068 representsand correspond to first orders 110, 112, 114, and 116 of FIG. 1.Similarly, second order 1070 represents and correspond to second orders124, 126, 128, and 130. FIG. 11 shows the diffraction generated from thegrating base 248 when the deflected beams (every third beamconfiguration) are moved to their secondary position where they arealigned with the undeflected beams. In this configuration impinginglight 1064 is concentrated in only the zero order, 1066 and first order(due to d spacing), 1072. It is important to note that FIGS. 10 and 11are simply illustrative of how light readings may be taken from thisgrating, and that many other variations obvious to someone of ordinaryskill are possible and clearly within the scope of this disclosure andits associated claims.

The reconfigurable compound diffraction grating 108 is typicallyfabricated using MEMS processing. Current MEMS processing techniques arecapable of features on the scale of 1–2 microns. The most criticaldimension in the operation of the diffraction grating is the width ofthe beam. The ruling or grating spacing determines the resolution of thegrating. With the current feature sizes on the 1–2 micron scale, agrating comparable with a medium resolution (600–1200 grooves/mm)conventional optical grating is produced. This resolution is ideal forthe visible and near-infrared region of the electromagnetic spectrum andhigher wavelengths, as well. The design of the reconfigurable compounddiffraction grating can be scaled to include wider beams and gratingspacings to be useful in applications in the infrared region of theelectromagnetic spectrum. As the size limitations of the MEMS processingtechnique decreases, the reconfigurable compound diffraction gratingwill be applicable to even shorter wavelengths, and it is contemplatedthat the scaling of the beam width and ruling to such smaller dimensionsis fully encompassed by this disclosure and its subsequent associatedclaims.

Alternative embodiments of the present invention of the WDM/DWDM systemprimarily utilize alternative configurations of reconfigurablediffraction grating 108. The design of the reconfigurable diffractiongrating presented in FIGS. 2 through 9 constitutes the best modepossible at present. However, alternative configurations of thereconfigurable diffraction grating that can be implemented in theWDM/DWDM system include variations in the configuration of beams thatestablish the rulings of the diffraction grating. The design presentedin the preferred embodiment of the WDM/DWDM system can be formed with avariety of beam widths and spacings between the beams, also known asgrating spacing. For example, these variations include but are notlimited to, beams spaced half a beam width apart, a quarter of a beamwidth apart, and twice a beam width apart. All such variations in thereconfigurable diffraction grating, and similar variations, arecontemplated by this disclosure and its associated claims.

Further, while the reconfigurable compound diffraction grating 108illustrated and discussed in detail in FIGS. 2 through 9 is the bestmode for compound diffraction grating 108 that can be used incombination with the multiplexer of FIG. 1, the use of any otherdiffraction grating known in the art possessing suitable size andoperational characteristics for use as element 108 in combination withthe overall multiplexing system shown in FIG. 1 is also fullycontemplated within the scope of this disclosure and its associatedclaims. This could include, for example, not limitation, any of thevarious diffractive elements referred to in the background of theinvention herein, as well as the diffractive elements disclosed in theseveral U.S. Patent referred to herein, to the extent that theiremployment for this multiplexing application may be feasible and useful.

That is, this disclosure and its associated claims broadly encompassboth a lightwave multiplexing system employing any suitablereconfigurable compound diffraction grating as element 108 in the mannerand combination disclosed in FIG. 1, as well as, more narrowly, alightwave multiplexing system employing the specific best mode of thereconfigurable compound diffraction grating disclosed in FIGS. 2 through9 as element 108 in combination with the overallmultiplexing/demultiplexing system disclosed in FIG. 1.

Another alternative configuration of the reconfigurable diffractiongrating 108 that could be beneficial to the design of the WDM/DWDMsystem for a specific implementation includes coating the set of beams256, the upper electrode lead 254, and the lower electrode lead 252,with a thin film of reflective coating such as gold or aluminum in orderto significantly increase the reflectivity and therefore resultantsignal strength. Coating the top surface of the set of beams 256, alsoprovides a means of reducing the electrical resistance. This isparticularly important in high frequency applications.

While only certain preferred features of the invention have beenillustrated and described, many modifications, changes and substitutionswill occur to those skilled in the art. It is, therefore, to beunderstood that this disclosure and its associated claims are intendedto cover all such modifications and changes as fall within the truespirit of the invention.

1. A combined optical wavelength division multiplexing and opticalswitching system, comprising: a reconfigurable diffraction grating (108)diffracting at least one input light beam (106) into diffracted lightbeams of N wavebands (110, 112, 114, 116) wherein N is an integergreater than zero; and further diffracting each of said input lightbeams (106) into diffracted light beams (110, 112, 114, 116) across Xdiffraction orders wherein X is an integer greater than zero, for eachof said N wavebands; at least X sets of at least N light output means(140,144) each, each one of said X sets corresponding with one of said Xdiffraction orders, and for each said diffraction order, each one ofsaid N light output means (120, 122) corresponding with one of said Nwavebands at said order; wherein: said N is greater than one; said X isgreater than one; for each given one of said X diffraction orders, allof the diffracted light beams (110, 112, 114, 116) of a given one ofsaid N wavebands, from all of said input light beams (106), are focusedon the one of said N light output means (120, 122) corresponding withsaid given waveband within the one of said X sets of output meanscorresponding with said given one of said X diffraction orders;diffraction beams (256) of said reconfigurable diffraction grating (108)are selectively movable relatively to one another; and saidreconfigurable diffraction grating (108) is reconfigurable to opticallyswitch at least one specified waveband to a specified subset of saidoutput means (120, 122) corresponding with a specified subset of saiddiffraction orders.
 2. A combined optical wavelength divisionmultiplexing and optical switching system, comprising: a reconfigurablediffraction grating (108) diffracting at least one input light beam(106) into diffracted light beams of N wavebands (110, 112, 114, 116)wherein N is an integer greater than zero; and further diffracting eachof said input light beams (106) into diffracted light beams (110, 112,114, 116) across X diffraction orders wherein X is an integer greaterthan zero, for each of said N wavebands; at least X optical detectors(142, 146), each one of said X optical detectors (142, 146)corresponding with and detecting diffracted light (110, 112, 114, 116)from one of said X diffraction orders, wherein: said N is greater thanone; said X is greater than one; for each given one of said Xdiffraction orders, all of the diffracted light beams (110, 112, 114,116) at said given diffraction order, from all of said input light beams(106), are focused on the optical detector (142) corresponding with saidgiven diffraction order; for each given one of said X diffractionorders, all of the diffracted light beams (110, 112, 114, 116) of agiven one of said N wavebands, from all of said input light beams (106),are focused on one of at least N light output regions (120, 122) of theoptical detector (140) corresponding with said given diffraction orderdiffraction beams (256) of said reconfigurable diffraction grating (108)are selectively movable relatively to one another; and saidreconfigurable diffraction grating (108) is reconfigurable to opticallyswitch at least one specified waveband to a specified subset of saidoptical detectors (142, 146) corresponding with a specified subset ofsaid diffraction orders.
 3. The system of claim 1 or claim 2, saidreconfigurable diffraction grating (108) comprising: a first pluralityof substantially parallel diffraction beams (256); a second plurality oflower electrode extension beams (362) each associated with,substantially parallel to, and beneath one of said diffraction beams(256), said second plurality being at most equal to said first pluralityin number; and voltage differential application means (252) for applyingselected voltage differentials between each of said lower electrodeextension beams (362) and its associated diffraction beam (256) tothereby move at least one diffraction beam (256) from an initialposition thereof to a deflected position thereof.
 4. The system of claim3, said voltage differential application means enabling the applicationof a plurality of voltage differentials to be applied to a correspondingplurality of subsets of said diffraction beams (256), said subsets ofsaid diffraction beams (256) comprising at least one of said diffractionbeams (256).
 5. The system of claim 1 or claim 2, further comprising areflective coating on upper surfaces of a plurality of diffraction beams(256) of said reconfigurable diffraction grating (108) and on at leastan upper surface of a base (248) of said reconfigurable diffractiongrating (108).
 6. The system of claim 1 or claim 2, wherein saidreconfigurable diffraction grating (108) is fabricated usingmicroelectromechanical systems technology.
 7. The system of claim 1 orclaim 2, wherein a ratio of spacing between each successive diffractionbeam of a plurality of diffraction beams (256) of said reconfigurablediffraction grating (108)to a width of each said diffraction beam (256)is substantially between ¼ to 1 and 2 to
 1. 8. The system of claim 1 orclaim 2, further comprising: optical input means (100) for delivering aninput source light beam (102) to said system; and means of collimating(104) said input source light beam (102) into said at least one inputlight beam (106) diffracted by said reconfigurable diffraction grating(108).
 9. The system of claim 1, each of said at least N output means(120, 122) of each said set of output means (140) comprising anindividual optical fiber.
 10. The system of claim 1, each of said atleast X sets of at least N light output means (140) comprising anoptical fiber bundle of at least N optical fibers.
 11. The system ofclaim 1, further comprising: at least X optical detectors (140, 146),each one of said X optical detectors (140, 146) corresponding with anddetecting diffracted light (110, 112, 114, 116) from one of said Xdiffraction orders, and also corresponding with and receiving diffractedlight from the set of at least N light output means (140) correspondingwith said one of said X diffraction orders, wherein: for each given oneof said X diffraction orders, all of the diffracted light beams (110,112, 114, 116) at said given diffraction order, from all of said inputlight beams (106), are received by the optical detector (142)corresponding with said given diffraction order over said set of atleast N light output means(120, 122) corresponding with said givendiffraction order; and for each given one of said X diffraction orders,all of the diffracted light beams (110, 112, 114, 116) of a given one ofsaid N wavebands, from all of said input light beams (106), are receivedby one of at least N light output regions (120, 122) of the opticaldetector (142) detecting said given diffraction order over the one ofsaid N light output means (120, 122) corresponding with said given oneof said N wavebands at said order.
 12. The system of claim 1 or claim 2,said at least one input light beam comprising more than one input lightbeam.
 13. A method of optical wavelength division multiplexing incombination with optical switching, comprising the steps of: diffractingat least one input light beam (106) into diffracted light beams (110,112, 114, 116) of N wavebands wherein N is an integer greater than zero,by selectively moving diffraction beams (256) of a reconfigurablediffraction grating (108) relatively to one another; further diffractingeach of said input light beams (110, 112, 114, 116) into diffractedlight beams across X diffraction orders wherein X is an integer greaterthan zero, for each of said N wavebands, also using said reconfigurablediffraction grating (108); providing at least X sets of at least N lightoutput means (140) each, each one of said X sets corresponding with oneof said X diffraction orders, and for each said diffraction order, eachone of said N light output means (140) corresponding with one of said Nwavebands at said order; for each given one of said X diffractionorders, focusing all of the diffracted light beams (110, 112, 114, 116)of a given one of said N wavebands, from all of said input light beams(106), on the one of said N light output means (140) corresponding withsaid given waveband within the one of said X sets of output means (140)corresponding with said given one of said X diffraction orders; andoptically switching at least one specified waveband to a specifiedsubset of said output means (120, 122) corresponding with a specifiedsubset of said diffraction orders by reconfiguring said reconfigurablediffraction grating (108); wherein: said N is greater than one; and saidX is greater than one.
 14. A method of optical wavelength divisionmultiplexing in combination with optical switching, comprising the stepsof: diffracting at least one input light beam (106) into diffractedlight beams (110, 112, 114, 116) of N wavebands wherein N is an integergreater than zero, by selectively moving diffraction beams (256) of areconfigurable diffraction grating (108) relatively to one another;further diffracting each of said input light beams (110, 112, 114, 116)into diffracted light beams across X diffraction orders wherein X is aninteger greater than zero, for each of said N wavebands, also using saidreconfigurable diffraction grating (108); providing at least X opticaldetectors (142, 146), each one of said X optical detectors (142, 146)corresponding with and detecting diffracted light (110, 112, 114, 116)from one of said X diffraction orders; for each given one of said Xdiffraction orders, focusing all of the diffracted light beams (110,112, 114, 116) at said given diffraction order, from all of said inputlight beams (106), on the optical detector (142) corresponding with saidgiven diffraction order; for each given one of said X diffractionorders, focusing all of the diffracted light beams (110, 112, 114, 116)of a given one of said N wavebands, from all of said input light beams(106), on one of at least N light output regions (120, 122) of theoptical detector (142) corresponding with said given diffraction order;and optically switching at least one specified waveband to a specifiedsubset of said optical detectors (142, 146) corresponding with aspecified subset of said diffraction orders by reconfiguring saidreconfigurable diffraction grating (108); wherein: said N is greaterthan one; and said X is greater than one.
 15. The method of claim 13 orclaim 14, comprising the further steps of: providing a first pluralityof substantially parallel diffraction beams (256) of said reconfigurablediffraction grating (108); providing a second plurality of lowerelectrode extension beams (362) of said reconfigurable diffractiongrating (108), each associated with, substantially parallel to, andbeneath one of said diffraction beams (256), said second plurality beingat most equal to said first plurality in number; and moving at least onesaid diffraction beam (256) from an initial position thereof to adeflected position thereof by applying selected voltage differentialsbetween said diffraction beams (256) and their associated lowerelectrode extension beams (362), using voltage differential applicationmeans (252).
 16. The method of claim 15, comprising the further step ofapplying a plurality of voltage differentials to a correspondingplurality of subsets of said diffraction beams (256), said subsets ofsaid diffraction beams (256) comprising at least one of said diffractionbeams (256), using said voltage differential application means (252).17. The method of claim 13 or claim 14, comprising the further step of:providing a reflective coating on upper surfaces of a plurality ofdiffraction beams (256) of said reconfigurable diffraction grating (256)and on at least an upper surface of a base (248) of said reconfigurablediffraction grating (108).
 18. The method of claim 13 or claim 14,comprising the further step of: fabricating said reconfigurablediffraction grating using microelectromechanical systems technology. 19.The method of claim 13 or claim 14, wherein a ratio of spacing betweeneach successive diffraction beam of a plurality of diffraction beams(256) of said reconfigurable diffraction grating (108) to a width ofeach said diffraction beam (256) is substantially between ¼ to 1 and 2to
 1. 20. The method of claim 13 or claim 14, further comprising:delivering an input source light beam (102) for multiplexing by saidmethod, using optical input means (100); and collimating said inputsource light beam (102) into said at least one input light beam fordiffracting (106) by said reconfigurable diffraction grating (108). 21.The method of claim 13, each of said at least N output means (120, 122)of each said each said set of output means (140) comprising anindividual optical fiber.
 22. The method of claim 13, each of said atleast X sets of at least N light output means (140) comprising anoptical fiber bundle of at least N optical fibers.
 23. The method ofclaim 13, comprising the further steps of: providing at least X opticaldetectors (142, 146), each one of said X optical detectors (142, 146)corresponding with and detecting diffracted light (110, 112, 114, 116)from one of said X diffraction orders, and also corresponding with andreceiving diffracted light (110, 112, 114, 116) from the set of at leastN light output means (140) corresponding with said one of said Xdiffraction orders; for each given one of said X diffraction orders,receiving all of the diffracted light beams (110, 112, 114, 116) at saidgiven diffraction order, from all of said input light beams (106), withthe optical detector (142) corresponding with said given diffractionorder, over said set of at least N light output means (140)corresponding with said given diffraction order; and for each given oneof said X diffraction orders, receiving all of the diffracted lightbeams (110, 112, 114, 116) of a given one of said N wavebands, from allof said input light beams (106), at one of at least N light outputregions (120, 122) of the optical detector (142) detecting said givendiffraction order, over the one of said N light output means (140)corresponding with said given one of said N wavebands at said order. 24.The method of claim 13 or claim 14, said at least one input light beamcomprising more than one input light beam.